The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
During operation of a motor vehicle, emissions are generated that are treated in an exhaust aftertreatment system in order to reduce harmful pollutants. These pollutants include uncombusted hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen (NOx), and particulate matter (PM), among others. Treatment of the exhaust gas typically includes a catalyst, such as an SCR (selective catalyst reduction) catalyst, which converts or removes the pollutants contained in the exhaust gas.
During the first few minutes after engine start-up, or during a “cold start,” the engine block and coolant temperatures are low. Accordingly, the exhaust gas is at a lower temperature, which reduces the efficiency of the catalyst compared to steady-state operation at higher temperatures.
Furthermore, modern heavy duty engines are typically turbocharged. As exhaust gas passes through the turbocharger, the exhaust gas temperature decreases due to thermal energy being extracted to a compressor and to warm up the turbine housing. This decrease in temperature delays the light-off of downstream oxidation catalysts and SCR (selective catalyst reduction) catalysts during a cold start. In some cases, approximately 90% gaseous emissions escape to a tailpipe before the downstream catalysts are warmed-up and functioning.
These cold start issues in exhaust aftertreatment systems are addressed by the present disclosure.